Insights into the effect mechanism of nano LiAl-LDHs on the early hydration of sulphoaluminate cement-based materials

Sulfoaluminate cement-based grouting material (SAGM) is broadly used to reinforce engineering structures. It requires a high water–cement ratio (> 0.6) to improve its fluidity and permeability. However, this would result in a slow rate of hydration and a prolonged setting time of SAGM. Our previous investigation demonstrated that nano lithium aluminum layered double hydroxides (LiAl-LDHs) can dramatically accelerate hydration and raise the total hydration heat of SAGM. At the same time, the exact mechanism is still unknown. In this study, nano LiAl-LDHs were added to a suspension of SAGM in a semi-permeable membrane, permitting the passage of ions and water, and the mechanism of nano LiAl-LDHs influencing early hydration of SAGM was investigated. According to the results, nano LiAl-LDHs with an average hydrodynamic particle size of 85 nm preferentially provided the crystal nuclei for the hydration product of calcium monosulphoaluminate (AFm). In cement slurry, nano LiAl-LDHs can release lithium and carbonate ions, and released lithium ions can interact with aluminum ions in an alkaline environment to speed up the dissolution of anhydrous calcium sulphoaluminate. Carbonate ions released from nano LiAl-LDHs promoted the dissolution of anhydrous calcium sulphoaluminate, resulting in the formation of AFt and CaCO3. The effect of nano LiAl-LDHs on the early hydration of SAGM can be attributed to the synergistic effects of crystal nuclei, lithium ions, and carbonate ions released from nano LiAl-LDHs.